The present invention relates to a hybrid vehicle constructed so that running drive can be effected by transmitting engine output through a gear-change mechanism to the vehicle and running drive is also possible by means of a drive motor that is arranged in parallel with the engine, so that, in prescribed operating conditions, the engine may be temporarily stopped and running drive may be performed by driving the vehicle by means of the drive motor.
Efforts are being made to put into practice hybrid vehicles wherein running can be performed using engine drive and electric motor drive in combination, with the object of improving engine fuel consumption etc. Such a hybrid vehicle is disclosed for example in Laid-open Japanese Patent Application Number H. 11-132321. This vehicle comprises an engine, a first motor generator connected to the engine crankshaft, a belt type infinitely variable gear-change mechanism connected to the engine output shaft through a torque converter, and a second motor generator connected to a power transmission system on the output side of this infinitely variable gear-change mechanism. This vehicle is arranged such that ordinary running is performed by converting the gear ratio of the engine driving force in the infinitely variable gear-change mechanism before transmitting it to the vehicle wheels; when the vehicle is temporarily stopped, the engine is also temporarily stopped; and when subsequently the vehicle is made to move off, the vehicle wheels are driven by a second motor generator. It should be noted that, when the vehicle is thus made to move off again, the engine is restarted by the first motor generator, and after the vehicle has moved off a changeover is effected to running using engine drive.
If the engine is thus stopped when the vehicle is temporarily stopped, hydraulic pump drive by the engine is also stopped, causing the hydraulic pressure of the infinitely variable gear-change mechanism to be lost. Accordingly, a second hydraulic pump is provided that is driven by an electric motor and when the engine is stopped a prescribed hydraulic pressure is generated by driving the second hydraulic pump by means of this electric motor so as to prepare for the next move-off in a condition with the gear ratio set to the maximum (LOW) to enable motive force transmission, by supplying this prescribed hydraulic pressure to the output pulley cylinder chamber of the infinitely variable gear-change mechanism. In this way, in a hybrid vehicle as described above, an improvement is sought to be achieved in respect of fuel costs by stopping the engine when the vehicle is temporarily stopped, and an improvement in respect of fuel costs is sought to be achieved by driving the vehicle wheels using the second motor generator on moving off.
Consideration has also been given, with the object of further improving the fuel consumption, to stopping the engine and performing running using the electric motor drive also when the vehicle is running at comparatively high speed. If in this case the conventional hybrid vehicle control described above is employed without modification, the following problems arise.
Conventionally, when the engine was stopped in a condition where the vehicle was temporarily stopped, it was arranged for the clutch, which is provided in the power transmission system, to be prepared for the next move-off by being in an engaged condition, by hydraulic fluid pressure supplied from the second hydraulic fluid pump during the engine stoppage. However, if the clutch is put in engaged condition when the engine is stopped during running, the problem arises that the gear-change mechanism and the torque converter are rotated by the driving force from the vehicle wheels, generating entrainment torque, necessitating additional driving torque from the electric motor, thereby lowering the drive efficiency.
Also, conventionally, the arrangement was such that, when the engine was stopped on temporary stoppage of the vehicle, the next move-off was prepared for in a condition with transmission of motive force being made possible by setting the gear ratio to the maximum (LOW), by supplying hydraulic fluid, supplied from the second hydraulic fluid pump, to the output pulley cylinder chamber of the infinitely variable gear-change mechanism. However, there was the problem that, if the engine was stopped during running and running drive effected using the electric motor, since control was performed such as to make the gear ratio the maximum (LOW), on return from electric motor drive to engine drive during running, since the gear ratio was the maximum (LOW) for the current vehicle speed, the engine speed had to be raised unnecessarily, impairing fuel consumption and drivability.
Accordingly, the present applicants gave consideration to performing gear ratio control such that the gear ratio of the infinitely variable gear-change mechanism should have a value corresponding to the current operating condition, by using hydraulic pressure obtained by driving the second hydraulic pump by the electric motor when running was performed with the engine stopped.
However, when the engine is temporarily stopped as described above, for reasons relating to battery capacity etc it is demanded to make the electric power consumption of the electric motor that drives the second hydraulic pump as small as possible; also, the delivery capacity of the second hydraulic pump is made as small as possible and the hydraulic pressure for gear ratio control is also made as low as possible. However, when gear-change control is performed using such a miniaturized second hydraulic pump, there is the problem that the rate at which gear change can be achieved is limited; for example in the case of sudden braking action whilst running, resulting in abrupt deceleration and stopping, gear change control in a manner such as to track this cannot be achieved i.e. gear change control displays a time-lag.
Specifically, for example, in a case where brake action is performed when running at comparatively high speed in a condition with the gear ratio close to the minimum (TOP), causing abrupt deceleration and stopping the vehicle, gear-change control is demanded whereby the gear ratio can be changed to the maximum (LOW) in the short time that elapses before the vehicle is thus abruptly stopped. However, since, as described above, the rate of gear-change that is achievable is reduced by miniaturizing the second hydraulic pump, the condition is generated that the gear ratio is left at an intermediate value, since the gear ratio has not been able to return to the maximum (LOW) by the time the vehicle has stopped, owing to the gear-change control lag.
In this situation, typically control is effected such that the engine is stopped when the vehicle is stopped, with the object of improving the fuel consumption; consequently, when the vehicle stops, the engine is stopped and the gear ratio remains at an intermediate gear ratio; thus, there is the problem that when the engine is started and the vehicle moves off moving-off control must be effected from an intermediate gear ratio, with the consequence that sufficient moving-off driving force is not obtained. Also, if, in order to obtain sufficient driving force, the gear ratio is returned to the maximum (LOW) before moving-off control is exercised, there is the problem that moving off is delayed, impairing drivability.
An object of the present invention is to provide a hybrid vehicle control device constructed such that fuel consumption and running performance are not impaired even when performing running drive wherein the engine is stopped and an electric motor is used during running at comparatively high speed.
A further object of the present invention is to provide a hybrid vehicle control device constructed such that it can cope with such gear-change requests even when abrupt gear-change requests are generated by for example abrupt deceleration during running with the engine stopped.
Yet a further object of the present invention is to provide a hybrid vehicle control device constructed such that miniaturization and weight reduction of the hydraulic pump that is driven by the electric motor during engine stoppage can be achieved.
According to the present invention, a hybrid vehicle is constituted comprising: an engine that is capable of temporary stoppage control in a prescribed operating condition, an infinitely variable gear-change mechanism (for example metal V-belt type infinitely variable gear-change mechanism 20) connected to the output shaft of this engine and whereby the output rotation thereof is subjected to infinitely variable change of gear ratio, means for control of engagement/disengagement (for example forwards clutch 14 and reverse brake 15) that perform this engagement/disengagement control using hydraulic force and that are arranged so as to be capable of engagement/disengagement between the engine output shaft and an input member of the infinitely variable gear-change mechanism, a driving force transmission system (for example, idler shaft 31, final drive gear 32, final driven gear 33, differential mechanism 34, and axle shafts 35 etc) that transmits the output of the infinitely variable gear-change mechanism to the drive wheels, and an electrically driven motor (for example second motor generator 50) capable of driving the drive wheels by being connected to this driving force transmission system, in which this control device further comprises: a first hydraulic pump that is driven by the engine; and a second hydraulic pump that is driven by an electric motor for pump drive, and a hydraulic pressure supply changeover control valve (for example, forward/reverse clutch control valve 73) that effects changeover control of supply of working hydraulic fluid in respect of the means for engagement/disengagement control. When performing running drive with the drive wheels driven by the engine, gear-change control is executed by the infinitely variable gear-change mechanism by means of hydraulic pressure from the first hydraulic pump. On the other hand, when the vehicle is being run with the drive wheels driven by the electrically driven motor and with the engine stopped in a prescribed operating condition, the means for engagement/disengagement control are released by stopping the supply of working hydraulic pressure to the means for engagement/disengagement control by using the hydraulic pressure supply changeover control valve, so that the second hydraulic pump is driven by the electric motor for pump drive and gear-change control is executed such that the gear ratio of the infinitely variable gear-change mechanism is made to have a value matching the current driving conditions, using the hydraulic pressure obtained from the second hydraulic pump.
If a control device of such a construction is employed, when the engine is temporarily stopped on the occurrence of a prescribed operating condition during running etc at comparatively high speed, supply of working hydraulic pressure to the means for engagement/disengagement is stopped, thereby releasing this, so, in drive of the vehicle wheels by the electrically driven motor, any possibility of occurrence of entrainment torque trying to rotate the power transmission device located on the engine side of the means for engagement/disengagement is eliminated, thereby improving drive efficiency. Also, when running is thus effected by the electrically driven motor on temporary stoppage of the engine, gear-change control of the infinitely variable gear-change mechanism is performed using hydraulic pressure obtained by the second hydraulic pump, so a gear ratio suitable for the running conditions at that time point is always set, and, subsequently, smooth changeover to engine drive from running drive using the electrically driven motor can be effected by restarting the engine, thereby enabling the fuel consumption and drivability to be improved.
According to a further aspect of the present invention, a hybrid vehicle is constituted comprising: an engine that is capable of temporary stoppage control in a prescribed operating condition, an infinitely variable gear-change mechanism connected to the output shaft of this engine and whereby the output rotation thereof is subjected to infinitely variable change of gear ratio, a drive force transmission system that transmits the output of the infinitely variable gear-change mechanism to the driven wheels, and an electrically driven motor (for example second motor generator 50) that is capable of driving the driven wheels and is arranged parallel with the engine, in which the control device further comprises a first hydraulic pump driven by the engine and a second hydraulic pump driven by an electric motor for pump drive. With this control device, in a prescribed driving condition, in running with the engine stopped, gear-change control is performed such that the gear ratio of the infinitely variable gear-change mechanism assumes a value matching the current driving conditions, using the hydraulic pressure obtained from the second hydraulic pump, the second hydraulic pump being driven by the electric motor for pump drive, and furthermore, when there is a request for a large gear-change that cannot be coped with by gear-change control using hydraulic pressure obtained from the second pump, the engine is started and the first hydraulic pump is driven, so that the hydraulic pressure obtained from this first hydraulic pump is used for gear-change control.
The control device may further comprise means for discrimination that compare the requested rate of gear-change requested in accordance with driving conditions with the maximum rate of gear-change that can be obtained by hydraulic pressure supplied from the second hydraulic pump, and which, if it is concluded by the means for discrimination that the requested rate of gear-change is larger than the maximum rate of gear-change, cause the first hydraulic pump to be driven by starting the engine. For example, the engine stoppage permission cancellation decision processing control shown in FIG. 10 may be referred to.
Using such a control device according to the present invention, when a request for an abrupt gear-change is generated by for example abrupt braking action during running with the engine temporarily stopped, the engine is restarted and the hydraulic pressure from the first hydraulic pump is employed for gear-change control, so even if the second hydraulic pump is miniaturized, it is possible to cope with a request for an abrupt gear-change. The second hydraulic pump can therefore be miniaturized and reduced in weight and, in addition, the electric motor that drives the second hydraulic pump can be miniaturized and its power consumption kept to a minimum.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.